This application is a national stage of a PCT International Patent application no. PCT/DK98/00285, filed on Jun. 29, 1998.
The invention concerns a method for the rinsing of especially filter plates for fly ash in an electro-filter built into a filter housing, by means of a cleaning medium which under pressure is sprayed on the plates via movable nozzles, whereby the plates are cleaned.
An electro-filter comprises a filter housing in which one or more rows of mutually parallel filter plates are mounted, and which are electrically charged for the trapping of dust particles which are contained in the flue gas which is led through the filter housing.
These dust particles, fly ash, are loosened from the plates by mechanical means and are precipitated so that they can subsequently be removed.
However, the filter must be periodically inspected, which is why the insides of the filter housing such as the plates must be thoroughly cleaned of dust before personnel can be sent inside to carry out the inspection. If such a cleaning has not been effected, the personnel will be exposed to a considerable health risk due to the dust.
The result is that considerable costs are connected with this thorough cleaning, which in turn involves great operational losses due to the relatively long period of time required for the cooling and the cleaning of the filter.
Normally, the cleaning is effected manually while maintaining strict security precautions and the use of respirators, protective clothing etc.
In order to remedy these disadvantages, efforts are made to mechanise and automate this cleaning as much as possible.
From the description of U.S. Pat. No. 5,221,297, an example of a cleaning plant is known which can rinse the filter plates in the filter housing without manual assistance.
The plant comprises a nozzle arrangement which, from the one side of the plates, sprays the plates with a diffuse jet from spray nozzles, and a reflection arrangement extending at the opposite side of the plates which reflects the jets so that all areas on the sides of the plates are rinsed as clean as possible.
Both the nozzles and the reflectors are moved in a synchronous manner by means of a co-operating chain drive.
However, this plant is not particularly efficient, and with the comprehensive chain drive for both nozzles and reflectors it constitutes a very complicated construction. Moreover, the mechanical parts are disposed inside the filter housing where they are exposed to the aggressive dust, which means that the mechanical parts must be made of expensive materials. The plant is therefore vulnerable and subject to operational disturbances because of the dust which is deposited on the driving mechanism.
From the description of U.S. Pat. No. 1,399,441, a plant is known for the cleaning of filter plates by means of cleaning fluid, gas, which via movable nozzles is directed towards the electrode in the form of an even stream or possibly in a pulsating manner.
However, this plant is unable to clean the filter housing of dust in a manner whereby the insides of the housing can be inspected without risk. Consequently, a further thorough cleaning is necessary so that the dust can be removed to such an extent that the inspection can take place.
The object of the invention is to overcome the drawbacks and disadvantages of the cleaning plants of this kind, and this is achieved according to the invention by a method whereby the cleaning medium consists of water, and the nozzles are displaced a given distance along the side edge of the filter plates while at the same time the nozzles are rotated.
In a surprisingly simple manner, there is hereby achieved a washing of the plates which is very effective and herewith water-saving.
The rinsing with cleaning water is effective due to the relatively great kinetic energy of the water, and the dust is bound by and flushed out with the water.
This makes it possible for the filter housing to be inspected without any need for a preceding further cleaning.
Furthermore, the method ensures that the nozzles are moved a given distance longitudinally with the plates during simultaneous rotation. The total movement of the nozzles provides a progressive rinsing, in that the concentrated jets will form a concentric jet path on the plates. There is hereby achieved the best possible cleaning effect, in that the circular strokes assume rising and falling radii during the movement. The rinsing interval is reduced to the shortest possible period of time, and at the same time herewith the water consumption falls to a minimum, in that water is not wasted on surfaces already cleaned. The setting and the adjustment of the displacement and rotation of the nozzles ensures that both the consumption of water and cleaning time become minimal.
By letting the nozzles spray the rear and the front of the plates during their movement, a uniform and effective cleaning of the plates is achieved.
By configuring the rinsing equipment as a pipe on which the nozzles are mounted, and by displacing the pipe during its simultaneous rotation, and by mounting the drive unit and the water supply pipe outside the filter housing, an operationally reliable plant is achieved in an efficient manner, in that all mechanical parts are disposed outside the filter housing, and are thus not exposed to disturbing influences from the dust.
By mounting the nozzles on the pipe in pairs, and at least a distance between the nozzles corresponding to the displacement of the pipe, an effective cleaning of the plates can be ensured, in that all the plates are sprayed in a completely uniform manner.
By mounting the nozzle pairs in a plane which forms an angle with the plane of the plates which corresponds to the spraying of the furthermost areas on the plates, during the rotation a spreading of the jets will be achieved which, during the greatest possible angle of incidence, results in a jet direction directed both forwards and rearwards in relation to the direction of displacement.
By setting the displacement and the rotation so that the jet path assumes a mutually uniform distance, a highly efficient cleaning of the plates is achieved.
By letting the displacement correspond to a whole number of spaces between the plates, a compact construction of the equipment will be achieved, which at the same time results in a high efficiency and a minimum consumption of power and water.
Finally, it is advantageous to use the equipment for washing the plate elements corresponding to plate elements in an electro-filter.